Molecular sieves are a class of important materials used in the chemical industry for processes such as gas stream purification and hydrocarbon conversion processes. Molecular sieves are porous solids having interconnected pores of different sizes. Molecular sieves typically have a one-, two- or three-dimensional crystalline pore structure having pores of one or more molecular dimensions that selectively adsorb molecules that can enter the pores, and exclude those molecules that are too large. The pore size, pore shape, interstitial spacing or channels, composition, crystal morphology and structure are a few characteristics of molecular sieves that determine their use in various hydrocarbon adsorption and conversion processes.
For the petroleum and petrochemical industries, the most commercially useful molecular sieves are known as zeolites. A zeolite is an aluminosilicate having an open framework structure formed from corner sharing the oxygen atoms of [SiO4] and [AlO4] tetrahedra or octahedra. Mobile extra framework cations reside in the pores for balancing charges along the zeolite framework. These charges are a result of substitution of a tetrahedral framework cation (e.g. Si4+) with a trivalent or pentavalent cation. Extra framework cations counter-balance these charges preserving the electroneutrality of the framework, and these cations are exchangeable with other cations and/or protons.
Synthetic aluminosilicate molecular sieves, particularly zeolites, are typically synthesized by mixing sources of alumina and silica in an aqueous media, often in the presence of a structure directing agent or templating agent. The structure of the molecular sieve formed is determined in part by solubility of the various sources, silica-to-alumina ratio, nature of the cation, synthesis conditions (temperature, pressure, mixing agitation), order of addition, type of templating agent, and the like.
Molecular sieves identified by the International Zeolite Associate (IZA) as having the structure code MTW are known. ZSM-12 is a known crystalline MTW material, and is useful in many processes, including various catalytic reactions. Accordingly, there is a continued need for new methods for making ZSM-12, particularly small crystal forms of this material.
Further, there is a current need to identify molecular sieves that are suitable for catalystic n-paraffin isomerization. High-quality lubricating oils are required for the operation of modern machinery and automobiles. Most lubricating oil feedstocks must be dewaxed in order to produce high-quality lubricating oils. Catalytic dewaxing has advantages over solvent extraction of waxes, and the former is a valuable hydrocarbon processing technique. Catalytic dewaxing may be accomplished by cracking and/or isomerization of n-paraffins in the feedstocks.
Some prior art catalytic dewaxing processes operate at relatively high temperatures and pressures, resulting in extensive cracking and the production of lower value light gases. Therefore, catalytic dewaxing by isomerization of n-paraffins at lower temperatures is desirable. Accordingly, there is a continued need for new catalysts having improved hydrocarbon isomerization selectivity and conversion.